Breech plug with primer pocket for converting a black powder gun to smokeless powder

ABSTRACT

The breech plug with primer pocket of the present invention converts a black powder propellant muzzle-loading gun to a smokeless powder propellant muzzle-loading gun by providing a close fitting primer pocket wall, a flush fitting extractor that also supports the primer&#39;s sides, and a primer pocket seat that is cut at an angle of 25 degrees from the perpendicular of the primer pocket wall to conform to the front face of the primer, such that when the primer is seated against the primer pocket seat, a gas seal is formed. A gas seal is also formed at the primer&#39;s side walls.

[0001] This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 60/235,493, filed Sep. 26, 2000, and Ser. No. 60/262,944, filed January 19, 2001.

[0002] The present invention relates generally to muzzle-loading firearms, and more particularly to a new type of breech plug and primer pocket that effectively seals the combustion chamber of a muzzle-loading gun so that high pressure smokeless gas propellants may be used due to the high pressure gas remaining inside the combustion chamber, rather than being allowed to escape, such as through the conventional flash hole of most conventional muzzle- loaders.

BACKGROUND OF THE INVENTION

[0003] Although the THOMPSON-CENTER brand 209×0.50 muzzle-loading gun uses a shotgun shell primer, the walls of the primer are not supported over all their surfaces by a close fitting backing of steel in the gun's breech. Gas therefore escapes because of the loose fit of the primer in the breech, and thus low gas pressure black powder propellants, or their low gas pressure substitutes, are all that can be safely handled in such guns due to the relatively low gas pressure they require. The THOMPSON-CENTER brand 209×0.50 muzzle-loader is referenced herein only as an example of a typical muzzle-loading gun.

[0004] Improvements in high pressure gas control and the use of high strength stainless steel in gun breeches has allowed the use of modern smokeless powder propellants that generate higher gas pressure in most guns, rather than low gas pressure black powder propellants, or their substitutes, with the exception being muzzle-loaders. Smokeless powder propellants have proven to be preferable to black powder propellants for many reasons. The ability to use smokeless powder propellants provides increased versatility by making a greater variety of propellants available for use in guns to meet the specific needs of any specific occasions. The hazards of escaping black powder or black powder substitute gases to the eyes of the gun user are eliminated, because the strength of breeches required to contain the higher gas pressures of smokeless powder propellants mandates that an effective seal against high pressure gas escape be present. The ease with which reloading can be accomplished is greatly increased, because the fowling or residue left in gun barrels by black powder, or its substitutes, is eliminated. Reliability is also increased to the extent that misfires become a thing of the past; they almost never happen with smokeless powders; whereas misfires plague many, if not most, black powder propellants, or their substitutes. The corrosion that is a partner of black powder propellants, or their substitutes, is eliminated. If a gun can handle modern smokeless powder propellants, greater accuracy and velocity are easily achieved, which makes the gun much more desirable and valuable. The hazards associated with the volatility, explosiveness, storage, and transport of black powder, or its substitutes, are also eliminated, and the legalities of black powder sales therefore need not be considered.

SUMMARY OF THE INVENTION

[0005] The breech plug with primer pocket of the present invention converts a black powder propellant muzzle-loading gun to a smokeless powder propellant muzzle-loading gun by providing a close fitting primer pocket wall, a flush fitting extractor that also supports the primer's sides, and a primer pocket seat that is cut at an angle of 25 degrees from the perpendicular of the primer pocket wall to conform to the front face of the primer, such that when the primer is seated against the primer pocket seat, a gas seal is formed. A gas seal is also formed at the primer's side walls, but to a lesser extent, because the primer swells or expands under gas pressure, and since the primer's front seals the propellant gases from further escape, the side walls of the primer are of lesser importance. Thus, the one thousandth or two thousandth clearance of the primer's side walls specified in the preferred embodiment of the present invention that follows allows easy ejection of the spent primer. More than the specified tolerance will cause WINCHESTER brand primers, for example, to leak around the primer walls.

[0006] A preferred embodiment of the present invention is a breech plug with primer pocket for converting a black powder propellant gun to smokeless powder propellants, comprising a smokeless powder propellant breech plug sized to be closely removably fit within the breech of a black powder propellant muzzle-loading gun, with a breech opening at a first end of the plug and a primer pocket at a second end of the plug, with apparatus to pass smokeless powder propellant gas from the primer pocket to the breech opening, wherein the primer pocket is substantially cylindrical in shape with a diameter of about 0.2435 to about 0.2450 inches that is open at the first end of the plug and that has a primer pocket seat at the opposite end in direct communication with the apparatus to pass smokeless powder propellant from the primer pocket to the breech opening, the primer pocket seat having apparatus that conform the shape of the primer pocket seat to the front face of a primer filled with smokeless powder propellant to form a gas seal between the primer pocket seat and the primer, and primer extractor apparatus flushly fitted against the primer pocket to support a primer wall and to eject a spent primer from the primer pocket.

[0007] Related objects and advantages of the present invention will be clear from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0008]FIG. 1 is a segmented side view of the breech plug with primer pocket and primer extractor of the present invention.

[0009]FIG. 2 is a left side view of the breech plug with primer pocket and primer extractor of FIG. 1.

[0010]FIG. 3A is a rear view of the primer extractor of the present invention.

[0011]FIG. 3B is a top view of the primer extractor of the present invention.

[0012]FIG. 4 is a side view of the primer extractor of the present invention.

[0013]FIG. 5 is a segmented bottom view of the left end of the breech plug with primer pocket of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Referring now to the drawing Figures, the machining procedures for producing the preferred breech plug with primer pocket 10 of the present invention for a THOMPSON-CENTER brand 209×0.50 muzzle-loading gun will be described for illustrative purposes, only.

[0015] The procedure starts with a non-heated 17-4 PH stainless steel rod 0.75 inches in diameter that will become the breech plug with primer pocket 10 of the present invention. Start with a convenient length of 17-4 PH. Place it in an indexing head on a milling machine and cut 0.25 inches of {fraction (7/16)} inch hex on one end. Place the rod into a true running chuck, and index to less than 0.001 inches runout at about three inches from the chuck. Face the end square. Center drill the end for a tailstock support and apply a tailstock support.

[0016] All dimension numbers that follow are in inches, unless stated otherwise. The primer pocket 18 dimensions given below are the most critcal aspects of the breech plug with primer pocket 10 of the present invention.

[0017] Using the lengths provided in FIG. 1, cut the rod to the specified diameters of 0.620, 0.681, and 0.691 inches. Thread the middle section (0.681 inch diameter) at 20 threads per inch, with a thread tool that is similar to the WITWORTH type thread form. Cut the threads to nearly full depth. With a 0.157 inch diameter drill, drill to a depth of 0.700 inch into the center of first end 14 of the rod. Then with a drill of {fraction (27/64)} inches, drill about ¼ inch into the center of first end 14 of the rod. With a ball nose end mill that has been ground to a diameter of 0.450 inches, round the resulting breech hole 16 in first end 14 to a depth of about 0.300 inches.

[0018] At the first end 14 of the newly appearing breech plug with primer pocket 10, use a parting tool and turn the diameter of the breech hole 16 to 0.450 inches, being sure the cuts are square, and that the length exceeds the overall length of the breech plug with primer pocket 10 illustrated in FIG. 1 (1.320 inches). The length at the {fraction (11/16)} inch shoulder should be about 1.115 inches. Be sure to leave excess length needed for the width of the parting tool to cut it off. Remove the rod from the lathe chuck and use a wire brush to clean up the thread. The rod should then screw into the threaded end of the THOMPSON-CENTER gun barrel. Anti-seize or lots of oil should be used, and if there is any bind, dimensions must be a slip fit. If the rod seats against the gun barrel shoulder, torque to 30 ft. lbs.

[0019] Place the rod into the indexing head of the gun with a less than tight fit, and with the head set on zero, level the lug of the gun barrel. Tighten the jaws on the indexing head. Remove the barrel by unscrewing it. Set the indexing head to −7 or −8 degrees, and cut the flats of a {fraction (7/16)} inch hexagon into the second end 12 of the rod.

[0020] Remove the rod from the indexing head and cut it off a measured length longer than the specified overall length for the breech plug with primer pocket 10 illustrated in FIG. 1 (1.320 inches). Place the threaded end into a four jawed chuck on the lathe and index it to less than 0.001 inch runout. Aluminum or brass shim is optional, 17-4 PH is tough even when non-hardened, and a little gentleness on the t-bar of the chuck will keep any damage from occurring.

[0021] Face the rod's second end 14 off the measured amount (FIG. 1) so that an overall length of 1.320 inches is obtained. Some muzzle-loading guns may require the length to be as short as 1.318 inches. Testing in each gun might be necessary. The rod must close in the gun when torqued with a 0.0015 inch feeler between the rod and the gun's breech face.

[0022] With the rod indexed at 0.001 inch or less runout, drill into the second end 12 face with a small center drill. Then drill to a depth of 0.320 inch with a #2 drill. With a boring tool that has a 25 degree lead angle, bore to a depth of 0.299 to 0.306 inch. The resulting diameter of primer pocket 18 must be 0.2435 inch to 0.2450 inch. The creation of primer pocket 18 is best achieved if done in more than one step.

[0023] The resulting 130 degree included angle is at the seat or bottom 26 of the primer pocket 18. This is the actual angle produced by cutting the sides and bottom of the primer pocket with a cutting tool having a 25 degree lead angle. The resulting shape of the primer pocket 18 seat or bottom 26 now conforms to the front of a smokeless powder primer, thus effecting a seal when a primer is placed in the primer pocket 18. The angle does not need to be exactly 25 degrees, but this seems to be the optimum angle from testing that has been done to date.

[0024] Drill a flash hole through the center of the resulting breech plug with primer pocket 10 with a #55 or a {fraction (3/64)} inch drill bit. Cut the specified primer rim countersink 28 and chamfer 30 into the second end 12, as illustrated in FIGS. 1 and 5. A primer extractor cut 17 square with a flat of the {fraction (7/16)} hexagon at the second end 12 must be cut into a flat of the hexagon at second end 12 of the breech plug 10 (FIG. 5). This will allow the primer extractor, discussed below, to be fit flush with the corresponding wall of the primer pocket 18, thereby supporting the primer's side wall as well, as illustrated in FIG. 1.

[0025] Heat treat the breech plug 10.

[0026] Screw the breech plug with primer pocket 10 into the gun's barrel, again well-lubed, and torque to 50 ft. lbs. The hardened metal is less likely to gall, and is dimensionally slightly smaller than the untreated metal. The extractor cut 17 should be square at the bottom of breech plug with primer pocket 10.

[0027] Measure the distance from the bottom of the extractor cut 17 to the bottom of the primer pocket 18. This distance is the height of the primer extractor 20 at the bottom of the 0.2435 inch diameter of the primer pocket 18. The overall height of the primer extractor 20 should be about 0.545 inch. If it is different on any gun, it must be made to match the specific gun in question.

[0028] Place the THOMPSON-CENTER gun barrel with the breech plug with primer pocket 10 in place in a suitable fixture and center a six millimeter carbide end mill to make the extractor cut 17 under the hexagon on the second end 12 of breech plug with primer pocket 10, in the lug area of the barrel. With lube, mill the breech plug with primer pocket 10 in place to a depth of 0.090 inch. Remove the barrel from the fixture and de-burr the newly made extractor cut 17.

[0029] The primer extractor 20 is mated to the diameter of the primer pocket 18, and supports a primer wall from expansion under high pressure. The primer extractor 20 can be of semi-circular or full circular design and still accomplish this end. If it is semi-circular, it must be fitted to bear against a solid surface in order to be stationary enough to support a primer, and its sides must be mated to a recess within the primer pocket, as illustrated in the drawing figures. While the idea of a circular extractor may have been utilized in the past with the extractors of some obscure rimfire cartridge chambers, its use for primers is entirely new. Also the diameter must match the primer pocket 18 exactly or be no greater than the maximum primer pocket 18 diameter listed above (not the less critical and considerably smaller diameter of the previously mentioned rimfire cartridge case).

[0030] Hacksaw or otherwise saw a piece of ¾ inch×¼ inch oil hardening tool steel to approximate the primer extractor 20 dimensions that are shown in FIG. 4.

[0031] Finish the dimensioning with an end mill so that all surfaces are square and so that the upper part of the primer extractor 20 is narrowed to about 0.230 inch.

[0032] Turn the primer extractor 20 so that the long part is verticle, and so the end or lip that will contact primers is clear of the vise. With an end mill or other cutter that is 0.244 inch in diameter, cut in such a manner that the center of the cut is along the center of the primer extractor 20 until the above-measured 0.545 distance is achieved in the most central part of the cut. Put a {fraction (5/16)} inch end mill in the machine and cut a countersink to match countersink 28 by moving the cutter about 0.015 inches forward and plunging 0.020 inches (or up to 0.027 inches).

[0033] The primer extractor 20 arm must be reduced in thickness from 0.130 to 0.090 on the front facing, breech-plug-touching surface so that it clears the breach plug with primer pocket 10 at the 0.130 inch thickness.

[0034] The bevel 22 must be milled; the exact angle is not critical. The length of the cut is specified in FIGS. 3 and 4.

[0035] A cut 24 for a primer extractor 20 limit screw must be made.

[0036] The primer extractor 20 must fit into the gun's breach while still installed in the gun barrel.

[0037] The area of primer extractor 20 that should touch a primer should be either very close or exactly flush with the primer pocket 18 walls. If not, light lapping should clean it up. For this reason, holding to the tightest tolerance on the primer pocket 18 diameter is best.

[0038] Heat treat the primer extractor 20, and clean and assemble the new parts and the gun.

[0039] The firing pin protrusion must not exceed 0.060 inch; 0.055 inch is sufficient.

[0040] If the boring tool with the 25 degree lead angle was used to create primer pocket 18 to a depth of 0.299 inch, which is a very shallow primer pocket 18, considerable force is necessary to close the gun's action when a primer happens to be on the long side of the tolerance scale (0.304 inch), with only moderate force required to close the action on a short primer (0.299 inch). On the other hand, if the primer pocket 18 is cut to a depth of 0.306 inch, short primers seal anyway, and no force is required to close the gun's action. Primers still seal on the seat or bottom 26 of the primer pocket 18. Evidently the force of the firing pin seals the primer pocket 18 by forcing a primer forward at the time of ignition. Even the longest primers in a sample of WINCHESTER brand W209 closed with no force in addition to the force normally needed to close the gun's action. All of them sealed with a 0.306 inch depth primer pocket 18. Also, when the primer pocket 18 is deepened to the maximum tolerance (which would appear to be the most practical), the primer rim counter sink 28 must be made correspondingly deeper also. A depth of 0.026 inch or 0.027 inch is then correct.

[0041] The information about primers is provided because there seems to be a lot of variation in the length of primers from just one company, not to mention all the brands not tested to date. There is much more variation among older primers of the same manufacturer than in newer ones. The point is that primers of different lengths all seem to seal in a slightly long 0.2435 inch to 0.245 inch diameter primer pocket 18 if the seat 26 has the 130 degree included angle (cut with a boring bar with a 25 degree lead angle) that conforms to the primer's frontal shape.

[0042] The procedure for loading the THOMPSON-CENTER brand 209-0.50 muzzle loader is the same as it would be for any break-open type firearm into which the conversion of the present invention has been fitted. The procedure would also apply to any falling block firearm into which the conversion of the present invention has been fitted. The conversion system of the present invention will work wonderfully well in falling block actions so long as the primer extractor 20 can be supported opposite a primer so that the primer is contained under pressure, and not allowed to expand beyond the dimensions of the primer pocket 18.

[0043] Bolt actions can also be fitted with the conversion system of the present invention. A circular prime extractor that encompasses and supports a primer through 360 degrees, fitting between a shortened breech and the bolt face may be beneficial because it allows the bolt to rotate in and out of battery, while keeping a primer fully supported. To load, one must always open or expose the action, thus exposing the breech. It is helpful to place a dummy primer into the breech and close the action. When reloading, the previous shot's spent primer will also suffice. This prevents smaller granules of certain types of propellant powders from falling through the flash hole and into the works of the gun.

[0044] In many instances the powder charge would need to be pre-measured or pre-weighed, with sabots being recommended.

[0045] The conversion system of the present invention can still be used with black powder, if one would so choose. 

I claim:
 1. A breech plug with primer pocket for converting a black powder propellant gun to smokeless powder propellants, comprising a smokeless powder propellant breech plug sized to be closely removably fit within the breech of a black powder propellant muzzle-loading gun, with a breech opening at a first end of the plug and a primer pocket at a second end of the plug with means to pass smokeless powder propellant gas from the primer pocket to the breech opening, wherein the primer pocket is substantially cylindrical in shape with a diameter of about 0.2435 to about 0.2450 inches that is open at the first end of the plug and that has a primer pocket seat at the opposite end in direct communication with the means to pass smokeless powder propellant from the primer pocket to the breech opening, the primer pocket seat having means that conform the shape of the primer pocket seat to the front face of a primer filled with smokeless powder propellant to form a gas seal between the primer pocket seat and the primer, and primer extractor means flushly fitted against the primer pocket to support a primer wall and to eject a spent primer from the primer pocket.
 2. The breech plug with primer pocket of claim 1 wherein the primer pocket and primer pocket seat was formed with a boring bar with a lead angle of about 25 degree at the second end of the plug to a depth of about 0.299 to about 0.306 inches.
 3. The breech plug with primer pocket of claim 1 wherein the length of the plug between the first and second ends is about 1.318 to about 1.320 inches.
 4. The breech plug with primer pocket of claim 1 wherein the plug is removably fit within the breech of a black powder propellant muzzle-loading gun with means to thread the plug into the gun's barrel. 